The present invention relates to a change-speed gearbox and method and, more particularly, to a change-speed gearbox having six forward gears and one synchronized reverse gear with two countershaft transmissions and only one countershaft in which "rocking out" of the motor vehicle is possible.
In a known change-speed gearbox of the type shown in EP-A3 00 61 845, one countershaft transmission comprises two individual main shaft gear wheels which are connected to the output shaft by a change-speed clutch. A countershaft double gear wheel which meshes by its two gear rims with, in each case, one of the two main shaft gear wheels is connected to the countershaft by a simple gear shift clutch. While one main shaft gear wheel is arranged rotatably on the output shaft, the other main shaft gear wheel is connected directly to the driving clutch engaged in first gear.
In contrast, four gear wheel stages for the other countershaft transmission are arranged in such a way that one gear wheel stage is situated, on one hand, axially between the driving clutches, on the other hand, the first countershaft transmission, and the three other gear wheel stages are situated on that side of the countershaft double gear wheel which is opposite to the driving clutches. The countershaft gear wheels of the last-mentioned three gear wheel stages are each rotatably fixed to the countershaft. The countershaft gear wheel adjacent to the countershaft double gear wheel is arranged in an axially displaceable manner and furthermore is provided with that clutch half of the shifting clutch of the countershaft double gear wheel which is on the shaft side.
The central gear wheel of the three countershaft gear wheels can be brought into tooth engagement with the intermediate gear wheel by displacing the intermediate gear wheel which makes with a toothed rim of a change-speed clutch sliding gear shift sleeve mounted displaceably in a rotatable fixed manner on the output shaft. A change-speed clutch connects the main shaft gear wheels meshing with the two axially outer countershaft gear wheels to the output shaft. Due to the transmission arrangement, the reverse gear in the known change-speed gearbox is not synchronized, and alternate shifting between the reverse gear and one of the two lowest forward gears simply by alternate engagement of the two driving clutches is not possible because, in the two lowest forward gears, the sliding gear shaft sleeve used in reverse gear as the main shaft gear wheel of the output shaft must couple one and the same main shaft gear wheel to the output shaft and be actuated into its neutral position relative to the two adjacent main shaft gear wheels in order to engage reverse gear.
In a known change-speed gearbox having two countershaft transmissions as shown in DE PS 3,131,139, one countershaft each is used for each of the two countershaft transmissions in addition to the associated frictional driving clutch. A reverse-gear countershaft gear wheel is arranged on one countershaft together with an associated shifting clutch and can be driven, via the intermediate gear wheel, by that main shaft gear wheel which is connected directly to the driving clutch engaged both in a normal reverse gear and in first gear. The first gear countershaft gear wheel is arranged on the other countershaft and is connected to this countershaft by a synchronized shifting clutch so as to mesh with a main shaft gear wheel of the other countershaft transmission. Both in the two lowest forward gears and in the normal reverse gear, the driving torque is transmitted via one and the same countershaft gear wheel, which is here connected by engagement of an associated change-speed clutch to its countershaft exhibiting the reverse-gear countershaft gear wheel and meshes with a main shaft gear wheel seated in a manner rotatably fixed manner on the output shaft. With this complicated transmission arrangement, it would be in principle be possible by additional engagement also of the shifting clutch of the reverse-gear countershaft gear wheel to effect a shift between the normal reverse gear and the second gear simply by alternative engagement of the two driving clutches.
An object on which the present invention is based consists essentially in providing a change-speed gearbox and method having six forward gears and one synchronized reverse gear and having two countershaft transmissions and only one countershaft in which "rocking out" of the motor vehicle, which has become stuck due to spinning driving wheels, is possible, i.e., rapid shifting between forward and reverse travel simply by alternate engagement of the two driving clutches.
Starting from a change-speed gearbox of the general type discussed above, the foregoing object has been achieved in an advantageous manner by connecting the reverse-gear countershaft gear wheel to the countershaft by a synchronized change-speed clutch containing the shifting clutch for the first-gear countershaft gear wheel. The main shaft gear wheel which is used for the main shaft gear wheel meshing with the intermediate gear wheel is connected directly to the driving clutch engaged in first gear and meshes with the first gear countershaft gear wheel.
In the change-speed gearbox according to the present invention, it is advantageous that the intermediate gear wheel and the first-gear countershaft gear wheel mesh with one and the same main shaft gear wheel and that this countershaft gear wheel is arranged next to the reverse-gear countershaft gear wheel. The result is that one change-speed clutch can be used for both the first gear and the reverse gear, and the intermediate gear wheel can be over-mounted in a simple manner at one casing wall. The internal shift condition of the transmission for "rocking out" can thus be simply produced by one change-speed clutch being actuated into the reverse gear position and a different change-speed clutch from the latter being actuated into that multi-position in which the gear wheel stage concerned transmits the driving torque to the output shaft both in reverse gear and in second gear.